1. Field of the Invention
The present invention relates to elastic wave devices.
2. Description of the Related Art
Elastic wave devices haven been widely used in cellular phones and other suitable devices.
For example, an elastic wave filter disclosed in International Publication No. 2012/086639 includes a multilayer body in which a high acoustic velocity film, a low acoustic velocity film formed with an insulation material, and a piezoelectric film are laminated in that order. An interdigital transducer (IDT) electrode is provided on the piezoelectric film.
An acoustic velocity of a bulk wave propagating in the high acoustic velocity film is larger than an acoustic velocity of a main mode elastic wave propagating in the piezoelectric film. An acoustic velocity of the bulk wave propagating in the low acoustic velocity film is smaller than the acoustic velocity of the main mode elastic wave propagating in the piezoelectric film.
However, in the elastic wave filter disclosed in International Publication No. 2012/086639, because the thickness of the piezoelectric film is small and the low acoustic velocity film formed with the insulation material is provided under the piezoelectric film, electric charge is caused to stagnate in the process of forming the IDT electrode on the piezoelectric film, which causes surge breakdown to occur between an electrode finger and a busbar of the IDT electrode or the like in some case. As such, ripples are likely to be generated in a pass band of the elastic wave filter. In addition, frequencies at which the ripples are generated, the magnitude of the ripples, and other factors are likely to vary.